Williams tube

The Williams tube, or the Williams–Kilburn tube after inventors Freddie Williams and Tom Kilburn, developed in 1946 and 1947, was a cathode ray tube used as a computer memory to electronically store binary data. It was the first random-access digital storage device, and was used successfully in several early computers.

Williams and Kilburn applied for British patents on Dec. 11, 1946 and Oct. 2, 1947, followed by US patent applications on Dec. 10, 1947 (U.S. Patent 2,951,176) and May 16, 1949 (U.S. Patent 2,777,971).

Working principle

The Williams tube depends on an effect called secondary emission. When a dot is drawn on a cathode ray tube by a beam of fast-moving electrons, the area of the dot becomes slightly positively charged and the area immediately around it becomes slightly negatively charged, creating a charge well. The charge well remains on the surface of the tube for a fraction of a second, allowing the device to act as a computer memory. The lifetime of the charge well depends on the electrical resistance of the inside of the tube.